Following a screen period for 2-3 menstrual cycles that includes a placebo-treated cycle, eligible women are randomized double-blind to the short-term or long-term treatment arm. Subjects are switched (double-blind) to placebo after 4 months or 12 months of sertraline treatment. All subjects continue the study for a total of 21 months and receive either sertraline or the matching placebo in this interval. Subjects whose symptoms return are given open-label sertraline without breaking the study blind. Subjects rate symptoms daily throughout the study using the Penn Daily Symptom Report. Other assessments are conducted at monthly intervals and include the Clinical Global Impressions Rating Scale, Sheehan Disability Scale, Hamilton Depression Rating Scale, Endicott Quality of Life Questionnaire and the Cohen Perceived Stress Scale. The overall duration of the study is expected to be 5-6 years.